1. Technical Field
The present invention relates to a mounting structure of an electronic component.
2. Related Art
Mounting techniques are used in mounting, on a substrate, electronic components such as semiconductor integrated circuit, in order to manufacture a circuit substrate mounted on various electronic apparatuses as well as liquid crystal devices. A liquid crystal display device, for instance, includes an integrated circuit (IC) chip for liquid crystal drive so as to drive the liquid crystal panel mounted thereon. This IC chip for liquid crystal drive may also be mounted directly on a glass substrate that constitutes the liquid crystal panel, or, may be mounted on a flexible substrate (FPC) which is mounted on the liquid crystal panel. A mounting structure mounted by the former technique is called a chip on glass (COG) structure, and a mounting structure mounted by the latter is called a chip on flexible print circuit (COF) structure. In addition to these mounting structures, a chip on board (COB) structure may also be used. In this structure, an IC chip is mounted on, for instance, a glass-epoxy substrate.
Substrates used for such mounting structures include lands (terminals) coupled to a wiring pattern, and electronic components used include bump electrodes for obtaining electric connection. Mounting structures of electronic components are formed by mounting electronic components on the substrates in a state in which the lands are coupled to the bump electrodes.
It has been desired that, in those mounting structures, electronic components be firmly and securely coupled to substrates. Particularly, in the case where there are pluralities of lands and bump electrodes, and where the lands are coupled to the bump electrodes, it is important that all the lands and bumps are coupled well, in order to ensure reliability.
However, since lands and bump electrodes are generally formed with metal, a mispositioning during bonding and a misalignment caused by a low aligning precision of lands and bump electrodes may result in a contact defect (conductive defect) originating from insufficient bonding strength between these lands and bump electrodes.
Moreover, a fluctuation in distance may be caused between lands and bump electrodes by a warping of electronic components such as substrates and ICs as well as by a fluctuation in the height of lands and bump electrodes being formed. This may result in an inability to obtain sufficient bonding strength between the bump electrodes and the terminals, causing a contact defect (conductive defect).
In order to prevent such disadvantages, what has been provided is a print circuit board that includes a conductive pattern having a trapezoid section, a metal conductive layer formed thereon, and multiple concavities and convexities applied on a surface of this metal conductive layer (refer to JP-A-2002-261407 for an example).
Such a print circuit board is said to provide improved mounting yield, due to the anchoring effect originating from the concavities and convexities on the metal conductive surface. The anchoring effect prevents connecting electrodes of a component (electronic component) from slipping or sliding and getting inclined on electrodes on the substrate, when pressure is applied during component mounting.
However, while the slipping, the sliding, and the inclination of connecting electrodes (bump electrode) arranged over the metal conductive layer are prevented by the anchor effect originating from the concavities and convexities of the metal conductive surface, the above-mentioned print circuit board does not have a structure that increases the bonding strength between the metal conductive substrate and the connecting electrode. Further, the structure does not increase the bonding strength between a plurality of electrodes. Consequently, occurrences of the mispositioning during bonding and the misalignment between electrodes (lands and bump electrodes) caused by low aligning precision therebetween may still result in a contact defect (conductive defect) originating from insufficient bonding strength between these electrodes. Moreover, the connecting electrodes are formed with metal, and therefore exhibit plastic deformation upon coupling. This means that, if the distance between the lands and the electrodes are not constant as described above, the connecting electrodes may have a low capability in absorbing the distance deviation with elastic deformation, and therefore the bonding strength between these electrodes may be insufficient. For this reason, the contact defect (conductive defect) may still occur as well.